feat: module of utilities for integration tests

[JyJyJcr]

Proposed changes

This PR adds test_util module, utilities for integration tests of Nginx modules. The utilities were moved from tests/log_test.rs, and fixed to use the bundled Nginx used in bindings, the install path of which is recorded in nginx-sys::metadata::NGINX_INSTALL_DIR.

Checklist

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• I have written my commit messages in the Conventional Commits format.
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[dekobon]

Hi there, once again thank you for all of your contributions. I talked over this PR with some of the other project maintainers and there is a strong opinion that this functionality may be better in another project/library that supplements ngx-rust. Would it be possible to do that rather than integrate it into the core SDK?

[JyJyJcr]

Of course possible (and I agree to split it from the core), but before changing let me clarify which is better, creating a new GitHub repository, or just separating it into a new subdirectory in this repository, just like nginx-sys?
Sidenote: we need to keep nginx-sys::metadata module to salvage build informations for integration tests in either case.

[bavshin-f5]

Sidenote: we need to keep nginx-sys::metadata module to salvage build informations for integration tests in either case.

There's nginx-sys::NGX_PREFIX that already contains the installation path (NULL-terminated u8 slice, so you need to strip the last byte and use std::os::unix::ffi::OsStrExt).

It's also optional and could be omitted by the buildsystem if you specify an empty --prefix (we do that for the official Windows builds), but that's only a problem with non-vendored Nginx source tree.

[JyJyJcr]

There's nginx-sys::NGX_PREFIX that already contains the installation path (NULL-terminated u8 slice, so you need to strip the last byte and use std::os::unix::ffi::OsStrExt).

Thank you for important information. Now test_util directly uses constants in bindings.rs (not only NGX_PREFIX but also other configurations, such as NGX_CONF_PATH).

[JyJyJcr]

Hi there, once again thank you for all of your contributions. I talked over this PR with some of the other project maintainers and there is a strong opinion that this functionality may be better in another project/library that supplements ngx-rust. Would it be possible to do that rather than integrate it into the core SDK?

Splitting the module to another project could cause incompatible (different version) two indirect dependencies to ngx crate. Such state would generate binding.rs twice, for two versions, resulting bad CI/CD performance.
Rather I add the feature test_util, and you can enable the module only in dev-dependencies.